Techniques that are based on an Internet protocol (IP) core network to implement a Layer 2 virtual private network (VPN) in a site, such as a data center, have been gaining popularity. Generally speaking, these types of techniques implement a core network, a site network, and an overlay network. In addition, the routing and forwarding information are maintained on the edge devices of sites without requiring that the core network and the site network be changed. The site network is a Layer 2 network with independent service functionality and is connected to the core network through one or more edge devices and is typically managed and controlled by a single organization. The site network mainly includes a host and a switching device, and an edge device provides Layer 2 switching functionality between sites. The overlay network is a virtual network created between the edge devices of a site, which provides a Layer 2 interconnection between site networks. The edge devices inform one another of the media access control (MAC) addresses of all of the hosts and routers that are connected to the respective edge devices, and form a larger Layer 2 forwarding domain by interconnecting a plurality of site networks. The core network is a network that is mainly carried by an IP routing device and that provides interconnection between site networks.